Documentation for 5.7 says it does create indexes for FKs automatically if one isn't created.
MySQL requires that foreign key columns be indexed; if you create a table with a foreign key constraint but no index on a given column, an index is created.
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https://dev.mysql.com/doc/refman/5.7/en/constraint-foreign-k...
Documentation for 5.7 says it does create indexes for FKs automatically if one isn't created.